Method and apparatus for cross polarization and cross satellite interference cancellation

ABSTRACT

A method and apparatus in which a Tap-Weight Computer (TWC) calculates a Tap-Weight Vector (TWV). The TWV is coupled to a register in each of a plurality of adaptive filter modules. Each such adaptive filter module includes several adaptive filters that each include a tapped delay line. The input to the tapped delay line of each such adaptive filter is one of a plurality of potential interfering signals. The TWV controls the weighting of the outputs from the taps off the delay line. The weighted outputs from each tapped delay line are then subtracted from a received signal which potentially includes interference from the potential interfering signals. The TWC is multiplexed to each of the plurality of adaptive filters so that each adaptive filter is loaded with a TWV calculated by the TWC to reduce the amount of interference contributed by a particular potential interfering signal coupled to an input to that particular adaptive filter. In one embodiment, a plurality of such adaptive filter modules share the same TWC.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of copending application Ser. No.13/192,821, filed Jul. 28, 2011, which claims the benefit of U.S.Provisional Patent Application No. 61/368,795, filed Jul. 29, 2010. Eachpatent application identified above is incorporated here by reference inits entirety to provide continuity of disclosure.

FIELD

The disclosed method and apparatus relate to interference cancellationin communication systems. Some embodiments relate to cancellation ofcross satellite and cross polarization interference.

BACKGROUND

Communications engineers face a number of challenges today, includingmaximizing the amount of information that can be communicated over thelimited resources available. With limited frequencies available overwhich to communicate radio signals, and with the amount of informationthat people wish to communicate growing rapidly, it is important to usethe available frequencies as efficiently as possible. In order to do so,it is necessary to provide means by which signal interference can bereduced to minimum levels in order to allow modulation of a maximumamount of information onto signals that are transmitted over thosefrequencies.

One area that has been of interest is that of satellite communications,especially satellite communications for delivery of media for consumerconsumption, such as television signals, or the like. As the number ofsatellites increase, the spacing, or separation between satellitesdecreases, and the increase in demand for more and more content to bedelivered from the same or multiple satellites, interference between thesatellite signals has become an issue.

One type of interference is due to the reception of signals transmittedfrom a first satellite at the same frequency or frequencies as signalsreceived from a second satellite. If a receiver receives both signalswithout being able to sufficiently discriminate between them, thesignals will interfere with one another. This is commonly referred to ascross-satellite interference. The closer the spacing between thesatellites, the more cross-satellite interference may occur. Conversely,the wider the antenna beam-width (which is equivalent to lower antennagain, i.e. a smaller antenna dish size), the more potentialcross-satellite interference.

Another type of interference is due to signals on a first polarizationof a first satellite being transmitted at the same frequency as desiredsignals on a second polarization of the first satellite. If the receiverreceives both and cannot sufficiently discriminate between the two, theneach will interfere with the other. This is referred tocross-polarization interference.

One way by which cross satellite and cross polarization interference canbe reduced is to put as much separation as possible between each pair ofpotentially interfering signals. Such separation may be, for example, byseparating the signals by frequency, physical distance, or the like.However, separating signals in these ways can reduce the amount ofinformation that can be transmitted between a transmitter and areceiver, because the efficiency with which information can betransmitted over the communication system may be diminished.Accordingly, it would be desirable to have effective means capable ofreducing the amount of cross satellite and cross polarizationinterference.

SUMMARY

The following presents a simplified summary of one or more embodimentsin order to provide a basic understanding of some aspects of suchembodiments. This summary is not an extensive overview of the one ormore embodiments, and is intended to neither identify key or criticalelements of the embodiments nor delineate the scope of such embodiments.Its sole purpose is to present some concepts of the describedembodiments in a simplified form as a prelude to the more detaileddescription that is presented later.

One embodiment of the presently disclosed method and apparatus providesa system in which a Tap-Weight Computer (TWC) calculates a Tap-WeightVector (TWV) that is coupled to a register in each of a plurality ofadaptive filters. Each such adaptive filter includes a tapped delayline. The input to the tapped delay line of each such adaptive filter isone of a plurality of a potential interfering signals. The TWV controlsthe weighting of the outputs from the taps off the delay line. Theweighted output from the tapped delay line are then subtracted from areceived signal which potentially includes interference from thepotential interfering signals. The TWC is multiplexed to each of theplurality of adaptive filters so that each adaptive filter is loadedwith a TWV calculated by the TWC to reduce the amount of interferencecontributed by a particular potential interfering signal coupled to aninput to that particular adaptive filter.

Because the interference is relatively time insensitive (i.e., does notchange significantly over short time intervals), the TWVs provided toeach adaptive filter can be calculated one at a time while holding eachof the other TWVs constant. Using several adaptive independent adaptivefilters allows the length of the TWV to be relatively small, making itrelatively simple to calculate the next TWV in the iterative process.

In one embodiment, the input to the delay line is a received signal thatincludes both the desired signal and one or more interfering signalsfrom the same satellite or from other satellites. Each potentiallyinterfering signal is weighted in accordance with the value of the TWVand subtracted from the received signal. An adaptive algorithm is usedto determine whether the weighting is ideal and to determine how toadjust the weighting to improve the cancellation of the interferencefrom each of the interfering signals.

Various embodiments of the disclosed method and apparatus for channelequalization are presented. Some of these embodiments are directedtoward systems and methods for cross polarization and cross satelliteinterference cancellation in a satellite environment.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosed method and apparatus, in accordance with one or morevarious embodiments, is described with reference to the followingfigures. The drawings are provided for purposes of illustration only andmerely depict examples of some embodiments of the disclosed method andapparatus. These drawings are provided to facilitate the reader'sunderstanding of the disclosed method and apparatus. They should not beconsidered to limit the breadth, scope, or applicability of the claimedinvention. It should be noted that for clarity and ease of illustrationthese drawings are not necessarily made to scale.

FIG. 1 is an illustrative example of an environment in which an adaptivefilter module that is controlled by a tap-weight computer may beadvantageously employed for reducing interference between a plurality ofsatellite signals.

FIG. 2 is a high-level block diagram illustrating an embodiment of anadaptive filter module that is controlled by a tap-weight computer forreducing or eliminating interference among received satellite signals.

FIG. 3 is a block diagram illustrating additional aspects of theembodiment of an adaptive filter module that is controlled by atap-weight computer of FIG. 2.

FIG. 4 is a block diagram illustrating another embodiment in whicherror-corrected signals are tapped at the output of each stage androuted to the computational block via a third multiplexer.

FIG. 5 is a block diagram illustrating details of an adaptive filterembodiment that may be used in the adaptive filter module that iscontrolled by a tap-weight computer of FIG. 2.

FIG. 6 is a block diagram illustrating an embodiment of the disclosedmethod and apparatus in which interference is cancelled from a pluralityof desired signals.

FIG. 7 illustrates the details of one particular adaptive filter modulein the context of a plurality of desired signals.

FIG. 8 is an electrical schematic diagram illustrating an example of anembodiment of a digital switch matrix.

FIG. 9 is a flow diagram of an embodiment of a method for determiningwhich satellite signals are interfering and need to be cancelled.

FIG. 10 is a flow diagram illustrating embodiment of a method fortesting for the amount of interference inflicted on the desired signalby the undesired signals.

FIG. 11 is a flow diagram illustrating yet another embodiment in which apredetermined or programmable subset of interference sources areprocessed.

FIG. 12 is a block diagram illustrating one implementation of atap-weight computer.

In the various figures of the drawings, like reference numerals are usedto denote like or similar parts.

The figures are not intended to be exhaustive or to limit the claimedinvention to the precise form disclosed. It should be understood thatthe disclosed method and apparatus can be practiced with modificationand alteration, and that the invention should be limited only by theclaims and the equivalents thereof.

DETAILED DESCRIPTION

One illustrative environment 10 of an environment in which an adaptivefilter module that is controlled by a tap-weight computer may beadvantageously employed for reducing interference between a plurality ofsatellite signals is shown in FIG. 1. The environment 10 is a typicalhome-cable-system installation; however, apparatuses and methods of thetype described herein may be equally advantageously employed in manyother environments, as well.

The environment 10 illustrates a system having two integratedreceiver/decoder (IRD) devices 12 and 14. An IRD convertsradio-frequency signals to a form that can be used in content displays,or the like. IRD devices include, for example, televisiontuner-receivers, single or twin tuner digital video recorders (DVRs),television receivers, single or multiple set-top boxes (STBs), serversthat distributes video signals to client boxes that feed displaydevices, or the like. The IRDs 12 and 14 may be of conventionalconstruction in order to operate in the cable distribution installation.

The IRDs 12 and 14 respectively receive intermediate frequency (IF)signals from an outdoor unit (ODU) 28 on cables 20 and 22 from a powerdivider 24. The power divider 24 is a two-way splitter which allowsbi-directional passage of both RF and DC signals to feed a signal havingcombined user bands (UBs) to each IRDs 12 and 14 in one direction and toprovide for the passing of command signals (for example DiSEqC™ signalsof the type described by the CENELEC EN 50494 standard commandstructure) between the ODU 28 and IRDs 12 and 14 in the other direction.The power divider 24 receives its input signal from a cable 26, which isconnected to the ODU 28, mounted, for example, on the roof or otherappropriate location on the house 11. The cables 20, 22, and 26 may beof any suitable cable construction, such as a coaxial cable, plasticoptical fiber (POF), or the like.

Typical ODUs include a parabolic dish or reflector and a low-noise block(LNB) 30 mounted on the feed of the dish. The LNB 30 may include an RFfront-end, a multi-switch, and/or other signal processing anddistribution equipment. The multi-switch and at least some of signalprocessing and distribution equipment may reside in a module remote fromthe LNB. The parabolic dish directs satellite microwave signals on whichmultiple television signals are encoded into the RF front end. Thesesignals are encoded with multiple television signals in multiplechannels, or transponders (typically 20-40 MHz wide each), over a verywide bandwidth (typically 500 MHz or 2 GHz wide bands). Also, the RFsignals are received in two polarizations (vertical and horizontal, orleft and right circular polarizations), effectively doubling thebandwidth.

The ODU 28 converts the received satellite microwave signals to a lowerfrequency over a smaller bandwidth that can be demodulated by anassociated IRD. In traditional systems the RF is converted down to IFbands. In the example illustrated, the ODU 28 includes an LNB 30, whichreceives microwave signals from one or more satellites 32-34 in asatellite constellation 35. The LNB 30 includes circuitry to receive thesatellite microwave signals and down-converts them to channels andfrequency-stacks them to appropriate UBs for delivery on cables 20 and22 to IRDs 12 and 14. This is referred to herein as “channelizing.”

As mentioned above, cross-satellite interference is due to the receptionof desired signals 36 transmitted from satellite 32 at the samefrequency or frequencies as unwanted signals 38 received from thesatellite 34 (and/or other satellites in the constellation, not shown).If a receiver receives both signals without being able to adequatelydiscriminate between them, the signals will interfere with one another.Cross-polarization interference is due to unwanted signals 40 on a firstpolarization from satellite 32 being transmitted at the same frequencyas the desired signals 36 on a second polarization from the satellite32. If the receiver receives both and cannot adequately discriminatebetween the two, then each will interfere with the other.

To address this issue, an example of an adaptive filter module that iscontrolled by a tap-weight computer 50, shown in FIG. 2, may be employedto substantially reduce or eliminate the interference among the receivedsatellite signals, including cross polarization and cross satelliteinterference. The adaptive filter module that is controlled by atap-weight computer 50 of FIG. 2 is a high-level block diagram, showingan instantiation of an adaptive filtering scheme applied to one of aplurality of channelized signals. Each of the channelized signals mayrepresent respective channel data received from the satellites of thesatellite constellation 35. In a typical installation, the adaptivefilter module that is controlled by a tap-weight computer 50 would bereplicated for each received channelized signal. Typically, the adaptivefilter module that is controlled by a tap-weight computer 50 may belocated in the LNB 30.

The adaptive filter module that is controlled by a tap-weight computer50 receives and channelizes signals from the satellite constellation 35by receiver and channelizer 52. The receiver and channelizer 50 producea number of outputs, each corresponding to a signal of the satelliteconstellation 35. The output of the satellite signal from which theinterference effects are to be removed is labeled d(n) and thepotentially interfering satellite signals are labeled x₁(n) . . .x_(m)(n). Each of the potentially interfering satellite signals x₁(n) .. . x_(m)(n) are connected to a respective adaptive filter 54 . . . 56.The adaptive filters 54 . . . 56 produce an error-correcting value thatis introduced into the desired signal d(n) by the interfering satellitesignals x₁(n) . . . x_(m)(n), that is subtracted from the desired signald(n) by a subtractor 58 to produce a circuit output signal D(n) that issubstantially without interference.

Each of the adaptive filters 54 . . . 56 includes a tapped delay line 60and a register 62. A tap-weight vector (TWV) is generated by atap-weight computer (TWC) 64, in a manner described in greater detail.The TWC receives an input from the output signal D(n) and another inputfrom the potentially interfering satellite signals x₁(n) . . . x_(m)(n),multiplexed in turn by a multiplexer 66 thereto. The TWVs generated bythe TWC are multiplexed in turn to the registers 62 by a multiplexer 68,which is synchronized with the multiplexer 66. The TWVs serve to adjustthe magnitude and phase errors of the respective potentially interferingsatellite signals x₁(n) . . . x_(m)(n).

FIG. 3, to which reference is now additionally made, is a block diagramillustrating additional aspects of the embodiment of an adaptive filtermodule 80 that is controlled by a tap-weight computer 64 of FIG. 2. InFIG. 3, an adaptive filter module 80 uses the following signalnomenclature:

d(n) as the input desired signal with interference signals,

x₁(n), x₂(n), . . . , x_(M)(n) as the interference signal inputs (i.e.digital samples),

and D(n) as the output desired signal with cancelled interferencesignals.

The adaptive filter module 80 includes a plurality of adaptive filters54, 55, . . . , 56. The adaptive filters 54, 55, . . . , 56 haverespective output signals labeled y₁(n), y₂(n), . . . , y_(M)(n). Eachof the adaptive filters 54, 55, . . . , 56 is optimized one at a time.That is, coefficients of each of the adaptive filters 54, 55, . . . , 56are sequentially computed by a tap-weight computer (TWC) 64. The TWC 64is connected to sequentially receive a respective one of the inputs x₁(n), x ₂(n), . . . , x _(M)(n) by a multiplexer 84 to compute a“tap-weighting vector” (TWV), having components W ¹, W ², . . . , W^(M), for the adaptive filter to which the respective input signal x₁(n), x ₂(n), . . . , x _(M)(n) is connected. Each TWV component W ¹, W², . . . , W ^(M), is calculated to adjust the coefficients of arespective adaptive filter 54, 55, . . . , 56 to result in the outputD(n) 82 of the adaptive filter module 80 having a minimum error power. Aleast-mean-square (LMS) algorithm may be used to compute the TWVcomponents W ¹, W ², . . . , W ^(M) that carry the string of values ofthe coefficients of the adaptive filters 54, 55, . . . , 56. Otheralgorithms, such as “method of steepest descent,” “recursive leastsquare,” “Newton's method,” or the like, may also be used to determinethe TWV. Once the coefficients of the adaptive filters 54, 55, . . . ,56 have been calculated, a TWV component W ¹, W ², . . . , W ^(M), isrouted via a multiplexer 86 to the corresponding adaptive filter 54, 55,. . . , 56. The multiplexers 84, . . . , 86 are synchronously operatedby a clock and timing circuit 88.

The outputs y₁(n), y₂(n), . . . , y_(M)(n) of the adaptive filters 54,55, . . . , 56 are subtracted from the input signal d(n) by subtractors90, 92, . . . , 94, producing respective error-corrected signals e₁(n),e₂(n), . . . , e_(M)(n). The error-corrected signals e₁(n), e₂(n), . . ., e_(M)(n) are the residue values, i.e., the square value of one term ata time is being minimized. Thus, the error-corrected signals are:

     e₁(n) = d(n) − y₁(n),     e₂(n) = e₁(n) − y₂(n),      ⋮  e_(M)(n) = e_(M) − 1(n) − y_(M)(n) = d(n) − y₁(n) − y₂(n) − … − y_(M)(n) = D(n)

It should be noted that the error-corrected signals e₁(n), e₂(n), . . ., e_(M)(n) at the outputs of the subtractors 90, 92, . . . , 94 fromindividual adaptive filter 54, 55, . . . , 56 are not multiplexed.Rather the error-corrected signals are cascaded, providing a savings inmultiplexers. This is possible because only one component of thecomposite error-corrected signal at a time is responsive to thecorresponding filter coefficient adjustments.

In the circuit of FIG. 3, a delay circuit 96 provides a delay thatapproximately matches the delay in the adaptive filters 54, 55, . . . ,56. In one embodiment, the delay of the delay circuit 96 is preset as adesign parameter. In another embodiment, the delay is programmable. Thevalue of the delay can be set anywhere from zero to NT, where N is thelength of an adaptive filter 54, 55, . . . , 56 and the T is the lengthof a clock cycle. A typical delay may be, for example, ½ NT (i.e. halfthe length of the adaptive filter). In the case in which satelliteinterference is being cancelled, the time delay between the desiredsignal and signals from interfering satellites is not expected to besufficiently significant as to warrant delay values outside the lengthof the filter N. In other embodiments however, a larger delay may bewarranted.

FIG. 4 shows another embodiment in which error-corrected signals e₁(n),e₂(n), . . . , e_(M)(n) in the adaptive filter module 80′ are tapped atthe output of each stage and routed to the computational block via athird multiplexer 91. All three multiplexers are synchronously operated.Clock and timing for the three multiplexers 84, . . . , 86 and 91 arenot shown for the sake of simplicity.

FIG. 5 shows the details of one of the adaptive filters 54, 55, . . . ,56, for example adaptive filter 54. The Z⁻¹ term denotes a delay by oneclock cycle T. The TWV components W ¹, W ², . . . , W ^(M) are stored bythe TWC 64 in weight setting registers 100 in corresponding adaptivefilters 54, 55, . . . , 56. Each TWV component W ¹, W ², . . . , W ^(M)is then provided by the weight setting registers 100 to a plurality ofweighting circuits 102, 104, . . . , 106 in each of the correspondingadaptive filters 54, 55, . . . , 56. Each of the weighting circuits 102,104, . . . , 106 adjusts the amount of the signal x(n) at each delaypoint that is to be summed together in a summing circuit 110 based onthe particular value of the TWV components W ¹, W ², . . . , W ^(M)associated with that weighting circuit 102, 104, . . . , 106.Accordingly, the output signal y(n) is the weighted sum of the variousdelays of x(n):

In FIG. 5:y(n)= w ₀*(n)x(n)+ w ₁*(n)x(n−1)+ . . . + w _(N-1)*(n)x(n−N+1);W (n+1)= W (n)+2μe*(n) x (n);

-   -   where e(n) is the residue error-corrected value,    -   μ>0 is the adaptation step size, where typical values are        between 2⁻⁹ to 2⁻⁶ (design parameter, programmable),    -   W(n)=[w ₀(n), w ₁(n), . . . , w _(N-1)(n)] is the tap-weight        vector value at time n, and    -   W(n+1) is the tap-weight vector next value at time n+1,    -   and where W is generalized representation of vectors W ¹, W ², .        . . , W ^(M).

It should be noted that in FIG. 3, the individual components (W ¹, W ²,. . . , W ^(M)) of the TVW are represented, and in FIG. 5, only one ofthe vector components is shown as an input to the weight settingregister 100, having its own complex composition.

In general, all terms in above equations are complex; the asterisk (*)denotes “conjugate complex number”. All multipliers are complex, as isthe case when the signals are complex (I, Q), such as with zero-IF ordirect down conversion in preceding stages. In most cases, the I and Qsignals are sent on separate wires; however, in some embodiments, the Iand Q signals can be multiplexed using sophisticated timing tosynchronize with the samples of the desired signals. There is a specialcase when all quantities above are real, as may be the case with real IF(not I, Q), e.g. with Low IF

In one embodiment in which only phase and amplitude of cancelling signalneeds to be adjusted, an adaptive filter of length N=1 may be used,degenerating to a single weight coefficient w ₀(n), which can berealized with a single complex multiplier.

In one embodiment, the weight coefficients (i.e., the TWV components W¹, W ², . . . , W ^(M)) are incremented (updated) only after P number ofsamples, averaging the values over P clock cycles to reduce the noise inthe error-corrected signal and improve the resolution. P is aprogrammable integer number in the range from 1 to 100 or more. Asliding window can be used in which one or more of the oldest samplefrom among the P samples is dropped and the newest added to the Psamples to be averaged.

FIG. 6 shows an embodiment of the disclosed method and apparatus inwhich interference is cancelled from a plurality of desired signals. Thedesired signals (with the associated interference) are designated as d₁,d₂, . . . , d_(K). The desired outputs with cancelled interference aredesignated as D₁, D₂, . . . , D_(K). The interference associated witheach desired signal d₁, d₂, d_(K) is cancelled by a signal generated ina respective one of a plurality of adaptive filter modules 80 ¹, 80 ², .. . , 80 ^(K). In the example shown in FIG. 6, K different adaptivefilter modules 80 ¹, 80 ², . . . , 80 ^(K) are shown, where K is avariable having an integer value.

In the embodiment shown, digitized bands from all satellites andinterference sources are channelized by channelizers 120 to extract allof the desired channels d₁, d₂, . . . , d_(K) and all of the interferingchannel vectors w ₁(n), x ₂(n), . . . , x _(M)(n) (for example satellitetransponders) and output them to a switch matrix 122. The channelizers120, however, are optional. In another embodiment, the entire band ofdesired and interfering signals may be processed, without channelizationinto individual channels.

The interference vectors x ^(i)=[x _(1i), x _(2i), . . . , x _(Mi)],i=1, 2, 3, . . . , K include a multiplicity of interfering signals x(n),as formulated below:

x¹(n) = [x₁₁(n), x₂₁(n), …  , x_(M 1)(n)]x²(n) = [x₁₂(n), x₂₂(n), …  , x_(M 2)(n)] ⋮x^(K)(n) = [x_(1K)(n), x_(2K)(n), …  , x_(MK)(n)]

where in x_(ji)(n), (j=1, 2, 3, . . . , M; i=1, 2, 3, . . . , K) aredigital samples of interfering signals, e.g. from adjacent satellitetransponders. While these signals interfere into desired signalsd_(i)(n), they may at the same time be also the desired signals, i.e.one or more of the d_(i)(n) signals that are processed in otherfiltering modules 80 ¹, 80 ², . . . , 80 ^(K).

Each of the K different adaptive filter modules 80 ¹, 80 ², . . . , 80^(K) share one TWC 64. Interference signal vectors x ¹, x ², . . . , x^(K), are of different lengths where there are K adaptive filter modules80 ¹, 80 ², . . . , 80 ^(K) used. That is, each interference signalvector x ¹, x ², . . . , x ^(K) comprises a set of interfering signals,the length M of each vector indicating the number of such interferingsignals in the vector. Accordingly, the vector x ^(i)=[x _(1i), x _(2i),. . . , x _(Mi)]; where i=1, 2, . . . , K. All terms (x) in thisequation are a function of n (sample time), which is not shown forsimplicity.

Three multiplexers 124, 126, and 128 provide an example of oneembodiment by which the TWC 64 may be shared among the plurality ofadaptive filter modules 80 ¹, 80 ², . . . , 80 ^(K). As can be seen inFIG. 6, the interference vectors x _(1i), x _(2i), . . . , x _(Mi) thatare applied to each adaptive filter module 80 ¹, 80 ², . . . , 80 ^(K)are coupled to the TWC 64 through the first multiplexer 124. The TWVcomponents W ¹, W ², . . . , W ^(M) are coupled to each of the adaptivefilter modules 80 ¹, 80 ², . . . , 80 ^(K) through the secondmultiplexer 126. The outputs D₁, D₂, . . . , D_(K) from each adaptivefilter module 80 ¹, 80 ², . . . , 80 ^(K) are then coupled back to theTWC 64 in order to allow the TWC 64 to determine whether furthercorrection to the TWV components W ¹, W ², . . . , W ^(M) is required(i.e., whether minimum error power has been achieved).

FIG. 7 shows the details of one embodiment of an adaptive filter module80 when used with a plurality of other adaptive filter modules of thetype shown in FIG. 6 It should be noted that the adaptive filter module80 of FIG. 7 may be identical to that of FIG. 3; however, the embodimentof FIG. 7 includes a coupling of the adaptive filter module 80 to themultiplexers 124, 126, and 128 of FIG. 6 The multiplexers insideadaptive filter module 80 are clocked synchronously at one rate (e.g.,the rate at which the TWV components W ¹, W ², . . . , W ^(M) areupdated). The multiplexers 124, 126, and 128 outside of the adaptivefilter module 80 are synchronously clocked, but at a different rate thanthe multiplexers 84, . . . , 86 inside the adaptive filter module 80(e.g., the rate at which the processing individual desired signals D(n)are updated).

FIG. 8 shows an example embodiment of a digital switch matrix 122 thatmay be used in the circuit of FIG. 6. As noted above, the digital switchmatrix routes desired and interference signals to the processingadaptive filter modules 80 ¹, 80 ², . . . , 80 ^(K) 150. The digitalswitch matrix operates by allowing any input to be connected to one ormore outputs simultaneously. However, each output can be connected toonly one input at a time. A series of cross-point switches 130 allowseach input to be connected to one output. Sixteen such cross-pointswitches 130 are shown in FIG. 8; however, it should be understood thatthe number of such cross-point switches is K times the number ofchannelized inputs, where K is the number of desired channels from whichinterference is to be cancelled.

FIG. 9, to which reference is now made, is a flow diagram 140 of anembodiment of a method for determining which satellites are interfering,i.e. which sources need to be cancelled. In this embodiment, theinterference from one adjacent satellite is initially evaluated, box142. An adaptive iteration process is used to evaluate whether theinterference is stopped when the amount that the error power changeswith each update of the TWV is below a preset threshold, or when thenumber of iterations reaches a preset value, box 144. Both the thresholdfor the change in error power and the number of iterations may beprogrammable. These two parameters can be used either alternatively orconcurrently. Next, the interference from a second adjacent satellite isevaluated, box 146. Next, the interference from a third satellite isevaluated, box 148, and so on.

FIG. 10, to which reference is now additionally made, is a flow diagram150, illustrating another embodiment. In this embodiment, interferingsignals are applied to an adaptive filter 80 and tested for the amountof interference they inflict on the desired signal, box 152. Apredetermined (programmable) threshold value may be used as a criteriato decide whether to process particular interference signal in theadaptive filter or not, box 154. Signals that do not cross thethreshold, i.e. when interference is negligible or nonexistent, aredisconnected from the filter, box 156, thus reducing the power andprocessing time of the computations.

FIG. 11 is a flow diagram 160 illustrating yet another embodiment inwhich a predetermined or programmable subset of interference sources areprocessed, box 162. A lookup table, for example, may be used with storedinformation on interfering signals may be used, box164.

FIG. 12 is a block diagram illustrating one implementation of a TWC 64.In the implementation of FIG. 12, the TWC 62 includes an input/outputsection 170 to receive at least the error-corrected signals e₁(n),e₂(n), e_(M)(n) and the input signals x₁(n), x₂(n), . . . , x_(m)(n),and to deliver the TWV components W ¹, W ², . . . , W ^(M). The inputand output signals are processed by a processor 172 in conjunction witha memory 174. The memory 174 may contain computer program steps toperform the methods and to produce the signals in a manner as describedabove. The term processor is intended to encompass any processing devicecapable of operating the system or parts thereof. This includesmicroprocessors, microcontrollers, embedded controllers,application-specific integrated circuits (ASICs), digital signalprocessors (DSPs), state machines, dedicated discrete hardware, or thelike. It is not intended that the processor be limited to any particulartype of hardware component implementation. For example, these devicesmay also be implemented as combinations of computing devices, forexample, a combination of a DSP and a microprocessor, a plurality ofmicroprocessors, one or more microprocessors in conjunction with a DSPcore, or any other such configuration. Moreover, the processing andcontrolling devices need not be physically collocated with the part ofthe system it serves. For example, a central processing unit orprogrammed computer may be associated with and appropriately connectedto each of the various components of the system to perform the variousactions described herein.

While various embodiments of the disclosed method and apparatus havebeen described above, it should be understood that they have beenpresented by way of example only, and should not limit the claimedinvention. Likewise, the various diagrams may depict an examplearchitectural or other configuration for the disclosed method andapparatus. This is done to aid in understanding the features andfunctionality that can be included in the disclosed method andapparatus. The claimed invention is not restricted to the illustratedexample architectures or configurations, rather the desired features canbe implemented using a variety of alternative architectures andconfigurations. Indeed, it will be apparent to one of skill in the arthow alternative functional, logical or physical partitioning andconfigurations can be implemented to implement the desired features ofthe disclosed method and apparatus. Also, a multitude of differentconstituent module names other than those depicted herein can be appliedto the various partitions. Additionally, with regard to flow diagrams,operational descriptions and method claims, the order in which the stepsare presented herein shall not mandate that various embodiments beimplemented to perform the recited functionality in the same orderunless the context dictates otherwise.

Although the disclosed method and apparatus is described above in termsof various exemplary embodiments and implementations, it should beunderstood that the various features, aspects and functionalitydescribed in one or more of the individual embodiments are not limitedin their applicability to the particular embodiment with which they aredescribed. Thus, the breadth and scope of the claimed invention shouldnot be limited by any of the above-described exemplary embodiments.

Terms and phrases used in this document, and variations thereof, unlessotherwise expressly stated, should be construed as open ended as opposedto limiting. As examples of the foregoing: the term “including” shouldbe read as meaning “including, without limitation” or the like; the term“example” is used to provide exemplary instances of the item indiscussion, not an exhaustive or limiting list thereof; the terms “a” or“an” should be read as meaning “at least one,” “one or more” or thelike; and adjectives such as “conventional,” “traditional,” “normal,”“standard,” “known” and terms of similar meaning should not be construedas limiting the item described to a given time period or to an itemavailable as of a given time, but instead should be read to encompassconventional, traditional, normal, or standard technologies that may beavailable or known now or at any time in the future. Likewise, wherethis document refers to technologies that would be apparent or known toone of ordinary skill in the art, such technologies encompass thoseapparent or known to the skilled artisan now or at any time in thefuture.

A group of items linked with the conjunction “and” should not be read asrequiring that each and every one of those items be present in thegrouping, but rather should be read as “and/or” unless expressly statedotherwise. Similarly, a group of items linked with the conjunction “or”should not be read as requiring mutual exclusivity among that group, butrather should also be read as “and/or” unless expressly statedotherwise. Furthermore, although items, elements or components of thedisclosed method and apparatus may be described or claimed in thesingular, the plural is contemplated to be within the scope thereofunless limitation to the singular is explicitly stated.

The presence of broadening words and phrases such as “one or more,” “atleast,” “but not limited to” or other like phrases in some instancesshall not be read to mean that the narrower case is intended or requiredin instances where such broadening phrases may be absent. The use of theterm “module” does not imply that the components or functionalitydescribed or claimed as part of the module are all configured in acommon package. Indeed, any or all of the various components of amodule, whether control logic or other components, can be combined in asingle package or separately maintained and can further be distributedin multiple groupings or packages or across multiple locations.

Additionally, the various embodiments set forth herein are described interms of exemplary block diagrams, flow charts and other illustrations.As will become apparent to one of ordinary skill in the art afterreading this document, the illustrated embodiments and their variousalternatives can be implemented without confinement to the illustratedexamples. For example, block diagrams and their accompanying descriptionshould not be construed as mandating a particular architecture orconfiguration.

While various embodiments of the disclosed method and apparatus havebeen described above, it should be understood that they have beenpresented by way of example only, and should not limit the claimedinvention. Likewise, the various diagrams may depict an examplearchitectural or other configuration for the disclosed method andapparatus. This is done to aid in understanding the features andfunctionality that can be included in the disclosed method andapparatus. The claimed invention is not restricted to the illustratedexample architectures or configurations, rather the desired features canbe implemented using a variety of alternative architectures andconfigurations. Indeed, it will be apparent to one of skill in the arthow alternative functional, logical or physical partitioning andconfigurations can be implemented to implement the desired features ofthe disclosed method and apparatus. Also, a multitude of differentconstituent module names other than those depicted herein can be appliedto the various partitions. Additionally, with regard to flow diagrams,operational descriptions and method claims, the order in which the stepsare presented herein shall not mandate that various embodiments beimplemented to perform the recited functionality in the same orderunless the context dictates otherwise.

Although the disclosed method and apparatus is described above in termsof various exemplary embodiments and implementations, it should beunderstood that the various features, aspects and functionalitydescribed in one or more of the individual embodiments are not limitedin their applicability to the particular embodiment with which they aredescribed. Thus, the breadth and scope of the claimed invention shouldnot be limited by any of the above-described exemplary embodiments.

Terms and phrases used in this document, and variations thereof, unlessotherwise expressly stated, should be construed as open ended as opposedto limiting. As examples of the foregoing: the term “including” shouldbe read as meaning “including, without limitation” or the like; the term“example” is used to provide exemplary instances of the item indiscussion, not an exhaustive or limiting list thereof; the terms “a” or“an” should be read as meaning “at least one,” “one or more” or thelike; and adjectives such as “conventional,” “traditional,” “normal,”“standard,” “known” and terms of similar meaning should not be construedas limiting the item described to a given time period or to an itemavailable as of a given time, but instead should be read to encompassconventional, traditional, normal, or standard technologies that may beavailable or known now or at any time in the future. Likewise, wherethis document refers to technologies that would be apparent or known toone of ordinary skill in the art, such technologies encompass thoseapparent or known to the skilled artisan now or at any time in thefuture.

A group of items linked with the conjunction “and” should not be read asrequiring that each and every one of those items be present in thegrouping, but rather should be read as “and/or” unless expressly statedotherwise. Similarly, a group of items linked with the conjunction “or”should not be read as requiring mutual exclusivity among that group, butrather should also be read as “and/or” unless expressly statedotherwise. Furthermore, although items, elements or components of thedisclosed method and apparatus may be described or claimed in thesingular, the plural is contemplated to be within the scope thereofunless limitation to the singular is explicitly stated.

The presence of broadening words and phrases such as “one or more,” “atleast,” “but not limited to” or other like phrases in some instancesshall not be read to mean that the narrower case is intended or requiredin instances where such broadening phrases may be absent. The use of theterm “module” does not imply that the components or functionalitydescribed or claimed as part of the module are all configured in acommon package. Indeed, any or all of the various components of amodule, whether control logic or other components, can be combined in asingle package or separately maintained and can further be distributedin multiple groupings or packages or across multiple locations.

Additionally, the various embodiments set forth herein are described interms of exemplary block diagrams, flow charts and other illustrations.As will become apparent to one of ordinary skill in the art afterreading this document, the illustrated embodiments and their variousalternatives can be implemented without confinement to the illustratedexamples. For example, block diagrams and their accompanying descriptionshould not be construed as mandating a particular architecture orconfiguration.

We claim:
 1. A method of cancelling interference from satellite signalsreceived at approximately the same frequency as a desired satellitesignal, comprising: receiving a composite signal comprising: a desiredsatellite signal at a frequency; a first interfering satellite signal atapproximately the frequency of the desired satellite signal; and asecond interfering satellite signal at approximately the frequency ofthe desired satellite signal; coupling a first register within a firstadaptive filter to a tap-weight computer; determining within thetap-weight computer an initial weight for each of several tapped outputsfrom the first interfering satellite signal; loading from the tap-weightcomputer a first tap-weight vector into the first register to controlthe amount to be adjusted of interfering signal at each of the tappedoutputs from the interfering satellite signal; determining a first errorcorrection of the composite signal based on the output of the firstadaptive filter; decoupling the first register and coupling a secondregister within a second adaptive filter to the tap-weight computer;determining an initial weight for each of several tapped outputs fromthe second interfering satellite signal; loading a second tap-weightvector into a register within a second adaptive filter to control theamount of interfering signal at each of the tapped outputs from thesecond interfering satellite signal; and determining a second errorcorrection of the composite signal based on the output of the secondadaptive filter.
 2. A system for reducing satellite signal interference,comprising: a receiver configured to receive a composite signalcomprising a desired satellite signal and a plurality of interferingsatellite signals, wherein the desired satellite signal and theplurality of interfering satellite signals are at approximately the samefrequency; a tap-weight computer (TWC) configured to compute atap-weight vector (TWV) for each of the plurality of interferingsatellite signals, wherein the TWV adjusts the magnitude and phase errorof its respective interfering satellite signal; a plurality of adaptivefilters, each adaptive filter configured to receive a respective one ofsaid interfering satellite-signals and a respective one of said TWVs forproducing an error-corrected signal, and a plurality of subtractors forsubtracting said plurality of error-corrected signals from saidcomposite signal to provide a desired system output signal; wherein saidTWC adjusts said TWVs to reduce interference from said interferingsatellite signals in said desired system output signal.
 3. The system ofclaim 2 wherein said TWC adjusts said TWVs using a least-mean-squarealgorithm.
 4. The system of claim 2 wherein said TWC adjusts said TWVsby minimizing a power level of said interfering satellite interferencesignals in said desired system output signal.
 5. The system of claim 2further comprising a delay element in an input path of said compositesignal in each of said adaptive filters.
 6. The system of claim 5wherein said delay element introduces a delay to said composite signalthat approximately matches a delay introduced by said plurality ofadaptive filters.
 7. A system for reducing satellite signalinterference, comprising: a receiver configured to receive a compositesignal comprising a desired satellite signal and an interferingsatellite signal, wherein the desired satellite signal and theinterfering satellite signal are at approximately the same frequency; atap-weight computer (TWC) configured to compute a tap-weight vector(TWV) for the interfering satellite signal, wherein the TWV adjusts themagnitude and phase error of the interfering satellite signal; anadaptive filter, comprising: a. a register into which said TWV iscoupled, b. a tapped delay line through which said interfering satellitesignal signal is clocked, said tapped delay line having a plurality ofoutputs, each output representing a term of said interfering satellitesignal, each output being delayed a predetermined number of clock cyclesfrom a next preceding output, c. a plurality of multipliers connected toproduce a product of a term of said TWV in said register and arespective one of said plurality of outputs to produce a plurality ofproduct outputs, and d. an adder to sum said plurality of productoutputs to produce an error-correcting signal, and a subtractor forsubtracting said error-correcting signal from said composite signal toprovide said desired satellite signal, wherein said TWC uses analgorithm to determine said TWV to reduce interference from saidinterfering satellite signal signal in said desired satellite signal. 8.The system of claim 7 wherein said predetermined number of clock cyclesis one clock cycle.
 9. The system of claim 7 wherein said algorithm is aleast-mean-square algorithm.
 10. The system of claim 7 wherein saidinterfering satellite signal is transmitted by a same satellite as saiddesired satellite signal.
 11. A system for reducing satellite signalinterference, comprising: a receiver configured to receive a compositesignal comprising a desired satellite signal and a plurality ofinterfering satellite signals, wherein the desired satellite signal andthe plurality of interfering satellite signals are at approximately thesame frequency; a tap-weight computer (TWC) configured to compute atap-weight vector (TWV) for each of the plurality of interferingsatellite signals, wherein each TWV adjusts the magnitude and phaseerror of its respective interfering satellite signal; a plurality ofadaptive filters, each comprising: a. a register into which acorresponding interfering satellite signal and TWV are coupled, b. atapped delay line through which a corresponding interfering satellitesignal is clocked, said tapped delay line having a plurality of outputs,each output representing a term of said corresponding interferingsatellite signal, each output being delayed a predetermined number ofclock cycles from a next preceding output, c. a plurality of multipliersconnected to produce a product of a term of said corresponding TWV insaid register and a respective one of said plurality of outputs toproduce an output product, and d. an adder to sum said output productsto produce an error-correcting signal output, and a plurality ofsubtractors for subtracting from said composite signal saiderror-correcting signal outputs of said plurality of adaptive filters toprovide said desired satellite signal, wherein said TWC uses analgorithm to cause said TWVs to reduce interference from saidinterfering satellite signals in said desired satellite signal.
 12. Thesystem of claim 11 wherein said TWVs are coupled to said registers by afirst multiplexer, wherein said interfering satellite signals aremultiplexed into said TWC by a second multiplexer, said first and secondmultiplexers being synchronized whereby a TWV is coupled to a registercontaining the interfering satellite signal to which said TWVcorresponds, and wherein said interfering satellite signal to which saidTWV corresponds is multiplexed into said TWC by a third multiplexer. 13.The system of claim 11 wherein said algorithm is a least-mean-squarealgorithm.
 14. The system of claim 11 further comprising a delay elementin an input path of said composite signal.
 15. , The system of claim 14wherein said delay element introduces a delay to said composite signalthat approximately matches a delay introduced by said plurality ofadaptive filters,
 16. A method for reducing satellite signalinterference, comprising: receiving a composite signal comprising adesired satellite signal and a plurality of interfering satellitesignals, wherein the desired satellite signal and the plurality ofinterfering satellite signals are at approximately the same frequency;generating a plurality of tap-weight vectors (TWVs) from saidinterfering satellite signals, wherein the TWV adjust the magnitude andphase error of its respecting interfering satellite signal; producing aplurality of error-corrected signals, each error-corrected signalcorresponding to a respective one of said interfering satellite signalsand a respective one of said TWVs; subtracting said plurality oferror-corrected signals from said composite signal to provide a desiredsystem output signal; wherein said TWVs are adjusted to reduceinterference from said interfering satellite signals in said desiredsystem output signal.
 17. The method of claim 16 wherein said TWVs areadjusted using a least-mean-square algorithm.
 18. The method of claim 16further comprising delaying said composite signal in an input path. 19.The method of claim 18 wherein said delaying comprises delaying saidcomposite signal for a time that approximately matches a delayintroduced by a plurality of adaptive filters, each adaptive filtercorresponding to one of the plurality of interfering satellite signals.